Cisepoxide

Cisepoxide, typically written as cis-epoxide or described as an epoxide derived from a cis-configured alkene, refers to an oxirane ring in which the two substituents originally on the double bond reside on the same face of the ring. This stereochemical outcome arises from syn additions during epoxidation, such that the relative configuration of substituents is preserved from the starting alkene.

In synthesis, cisepoxides are most commonly formed by syn epoxidation of cis alkenes. Reagents such as meta-chloroperbenzoic acid (mCPBA) or dimethyldioxirane (DMDO) can deliver the epoxide with retention of the original cis relationship. Catalytic asymmetric methods, including Sharpless, Jacobsen–Katsuki, and Shi epoxidations, enable enantioselective access to cis epoxides from suitable substrates, expanding their use in enantioselective synthesis. By contrast, trans alkenes furnish transepoxides under similar conditions.

Reactivity and applications: Epoxides are strained three-membered rings, making them reactive toward nucleophilic ring opening. For cisepoxides, the stereochemical course of opening can differ from that of transepoxides, particularly under acidic versus basic conditions, influencing regioselectivity and the configuration of products. Openings of cisepoxides commonly yield 1,2-diols or other fragments that retain stereochemical information useful for downstream synthesis.

Significance: Cisepoxides serve as versatile intermediates in organic synthesis, including natural product and pharmaceutical chemistry, where controlled stereochemistry in intermediate steps is essential. The term cisepoxide is less standardized in formal literature, with cis-epoxide or epoxides from cis alkenes being the more typical phrasing.